1. Field of the Invention
The present invention relates to a method for securing the authenticity of digital data.
2. Description of the Related Art
In recent years, an image (video) input apparatus, such as a digital camera, configured to digitize captured information and record the captured information on a recording medium as digital data has been widely used instead of a conventional silver-halide film camera or 8 mm-film camera. By using such a digital image input apparatus, a user can transmit the captured information itself to an information processing apparatus, such as a personal computer (PC), and display the captured information thereon. In addition, the user can momentarily transmit image data to anywhere around the world by transmitting the image data via a communication line.
Under such circumstances, an insurance company may utilize digital data to capture an image of an evidence for an accident. In addition, a construction company may utilize digital data to record progress at a construction site.
However, digital image data may be easily altered by using a commercial photo retouch tool. Accordingly, the authenticity of digital data is lower than that of a silver halide photograph. Therefore, the admissibility of digital data as evidence is very low.
In order to solve the above-described problem, U.S. Pat. No. 5,499,294 discusses a method in which secret information is previously held in a digital camera. In this method, when image data is captured by the digital camera, digital signature is provided to the captured image data within the digital camera by using the secret information. By executing verification processing using generated signature information after the shooting, the authenticity of the captured image data can be secured.
Meanwhile, in an image (video) input apparatus such as a digital camera, an electric signal of a captured image, which has been acquired by photoelectrically converting an optical image of the object by using an imaging device such as a complementary metal oxide semiconductor (CMOS) or a charge-coupled device (CCD), is converted into digital data by executing analog-to-digital (AD) conversion on the signal. Furthermore, the image data (hereinafter referred to as “RAW image data”), which has been converted into digital data, is subjected to various image processing. Thus, the image data is reproduced. Here, the image reproduction processing includes gamma correction processing, contrast correction processing, and white balance correction processing, for example.
In this regard, in particular, a recently marketed digital camera includes an operation mode for outputting the above-described RAW image data without executing any image processing thereon. When such a digital camera is used, the user transmits the RAW image data to a PC and uses an application installed on the PC to image-process the RAW image data. Thus, the image of the RAW image data is reproduced. Accordingly, the user is enabled to reproduce a desired image.
However, the method discussed in U.S. Pat. No. 5,499,294 does not discuss a method for executing image reproduction processing on the above-described RAW image data. That is, when image reproduction processing is executed on the PC, a digital signature that is provided on the RAW image data within the digital camera cannot be appropriately verified.
More specifically, when the method discussed in U.S. Pat. No. 5,499,294 is used, even when image reproduction processing, which is different from malicious alteration, is executed, the image reproduction processing may be determined as alteration. Accordingly, in the above-described conventional method, it is difficult to secure the authenticity of image data that has been subjected to image reproduction processing.